Field of the Invention
The present invention relates to a disc-based storage media, and more particularly, to an improved apparatus and method for determining the rotor position and driving such a device.
Computer systems often employ disc-based storage media to store and then retrieve data responsive to calls from the computer operating system. Conventional examples of such media include hard drives or floppy drives which store data to and retrieve data from the disc using a magnetic head positioned adjacent the magnetic disc. A brushless DC motor is widely used as the motor for rotating such a disc. The brushless DC motor includes a stator and a rotor having at least one permanent magnet. The motor is driven using an electromagnetic force generated by providing a current to a stator pole facing the rotor. In this case, it is necessary to detect the position of the rotor pole so that the electromagnetic force works effectively on the rotor pole. To this end, a detector directly fixed on a rotor shaft is used. A semiconductor switching device, such as a transistor or a thyristor, is turned on or off thus determining the commutation state according to the detected position of the rotor pole. Accordingly, torque for rotating the motor is continuously generated.
Various methods for detecting the position of a rotor pole have been proposed. Among them, a method using a hall sensor which is small and practical is most widely known. However, the hall sensor has a poor temperature characteristic and a defect ratio higher than a transistor.
Thus, currently, instead of using the hall sensor, a method for determining the position of a rotor pole by directly or indirectly detecting a back EMF (electromotive force) generated from the motor is widely used. Such methods are disclosed in U.S. Pat. No. 5,382,889, entitled "Self-commutating, back-EMF, brushless DC motor controller" by Peters et. al, and U.S. Pat. No. 5,028,852, entitled "Position detection for a brushless DC motor without hall effect device using time differential method" by Dunfield et. al.
In the aforementioned methods, the position of a rotor pole is estimated by measuring a voltage generated when a spindle motor rotates. Rotation of the spindle motor causes a back EMF or current to flow along the winding of a stator, thereby causing the motor to rotate in a predetermined direction.
However, according to those conventional methods, it is difficult to rotate the motor in a predetermined direction during an initial start-up stage of the motor because there is little information on the position of the rotor pole. In other words, in a state where the motor rotates, since a large voltage is generated, it is possible to control the motor to rotate in a predetermined direction by detecting the position of the rotor pole. However, since little voltage is generated at the start-up time of the motor, it is difficult to control the motor to rotate if in a proper direction.
In magnetic disc-based media, it is very important to rotate the disc in a proper direction during the initial start-up stage of the motor. If the disc rotates reverse to its normal direction, the disc can be scratched, thus damaging the surface of the disc. Furthermore, the start-up time of the motor increases if the disc is initially rotated in the wrong direction. This is because a voltage must be applied again to first stop the motor from rotating in the wrong direction, and then rotate the motor in the correct direction. Thus, a motor start-up circuit should be constructed so that a proper rotational direction can be determined by detecting the position of the rotor pole before starting up the motor. The motor start-up circuits which have been known up to now have been very complicated, which is an impediment to achieving light motor driving ICs.
Accordingly, the need exists for a simple method and apparatus for determining the proper rotational position and direction of the rotor pole and driving such a rotor pole.